System and method of supporting structural foundations

ABSTRACT

A system and method for supporting a structural foundation supported by a subterranean earth strata. A plurality of support piling segments are disposed in a columnar array beneath the foundation. Each segment has a central channel for receiving a tension or reinforcing member. The distal end of the tension member is anchored beneath the first or lowermost segment in the array. The anchor is sized such that it may not be withdrawn or pulled up through the channels in the segments. After the desired depth of the column is reached, a tension adjustment mechanism is affixed to the proximal end of the tension or reinforcing member and tightened to provide additional compressive force and strength to the columnar array.

This application claims priority to co-pending U.S. Provisional Application Ser. No. 60/489,403, filed Jun. 24, 2003.

FIELD OF THE INVENTION

This invention pertains to the field of lifting, repairing, leveling, and supporting structural foundations, more particularly the field of driving piling segments on top of each other into the earth beneath a structural foundation to form a columnar array or piling for supporting the foundation.

BACKGROUND OF THE INVENTION

Currently available methods of constructing columns and pilings underneath existing structural foundations share many features. Most drive, one at a time, with a jack, precast concrete segments with centrally located longitudinal holes into soil beneath a foundation. In some embodiments all the segments are slid onto a cable or strand that is epoxied into the first segment and extended out the piling top as the segments are driven to the ultimate depth; in others, reinforcing rod is inserted through the segment holes after the piling is complete. In either case, jacking is stopped and the piling is completed when a desired combined vertical reactive and friction force equals a predetermined jacking force. The piling is generally completed by placing a cap on top of the topmost piling segment, jacking the foundation up from the cap to its desired position, placing spacers and shims between the cap and foundation, removing the jack, and backfilling the space between the piling, cap, spacers, and foundation.

A weakness common to the state-of-the-art foundation support systems is a lack of lateral stiffness in the finished pilings. The requirement of providing support under an existing structure in most cases precludes the use of a continuous, one-piece piling. Construction of a piling with successive stacking of short segments makes possible the lifting and support of an existing foundation, but the resulting stack is likely to be unstable over time. Although the finished stacked piling is essentially embedded in a hole and surrounded by soil, the soil may not be stable. In many cases the foundation to be supported was in need of repair precisely because the underlying soil had shifted due to clay content, seasonal moisture variations, water table fluctuations, neighborhood blasting, or seismic events.

The introduction of a reinforcing rod or cable into the central hollow portion of a segmented piling, even with subsequent filling of the hollow with epoxy or grout, while improving initial alignment of the piling segments, adds little to the lateral stiffness or columnar strength of the completed piling.

SUMMARY OF THE INVENTION

Applicants' invention is a support system and process for installing post-tensioned segmented support pilings under structural foundations. By applying tension to a reinforcing member that extends the full length of the piling, all the segments are put into compression, essentially converting the stack or column into a continuous entity. Such post-tensioning and compression provide significantly more resistance to shear stress than epoxy or grout injected into the central conduit of the segments. Applicants' post-tensioned pilings resist shifting underground strata more successfully and for longer periods than currently available pilings. The unique anchor structure significantly reduces the likelihood that the tensioning member extending through the segments will be pulled through and out any of the segments in the column.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cylindrical or rectangular concrete piling segment, a reinforcing member and a threaded coupling inserted through the segment's central channel, and an anchor mechanism that prevents travel of the reinforcing member back through the segment hole.

FIG. 2 shows the invention in place with a first piling segment being driven, a second segment awaiting placement and a reinforcing member extending through the segments.

FIG. 3 shows a completed piling column with numerous segments, a reinforcing member tensioned with a tension adjustment at the top of the column and an anchor at bottom of the column, a piling cap, and two spacer blocks.

FIG. 4 illustrates an alternative embodiment with a plurality of reinforcing members attached to a bridle.

FIG. 4A is a view taken along line 4A-4A of FIG. 4.

FIG. 5 illustrates yet another embodiment wherein reinforcing members extend along external slots in the segment as well as through the central conduit.

FIG. 5A is a view taken along line 5A-5A of FIG. 5.

FIG. 6 shows an embodiment with a large washer anchor and a bullet nose cover.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the first end (10) of a reinforcing member (14) completely inserted through the substantially centrally located channel (18) in the body (17) of the segment (12 a). The channel (18) is substantially parallel with the longitudinal axis L of the first piling segment (12 a), the axis L being substantially vertical when the first piling segment is in its final installed position. The reinforcing member (14) has a second end (11) which will extend from the top of the last or uppermost segment when the column is completed. The member (14) has a length longer than the anticipated height of the final piling column. The reinforcing member may be cable, rod, bar, or any other suitable material for providing columnar strength to the support as will be described further.

An anchor mechanism (20) is attached to the protruding first end (10) of the reinforcing member (14), the anchor is sized to prevent the withdrawal of the first end of the reinforcing member back through the piling segment channel.

FIG. 2 shows a portion of excavated subterranean strata or earth (23) beneath the area of the structural foundation (22) to be supported at least sufficient to accommodate a jacking pump (24) and jack (25), a slotted guide block (if needed) (not shown), and the first piling segment (12 a). The first piling segment (12 a) is placed into excavated earth beneath the structural foundation (22) to be supported. As needed a slotted guide block (well known in the art) is slid onto the reinforcing member (14) and the guide block is placed on top of the first piling segment. The guide block serves to first guide the reinforcing member angularly away from the jack (25) and to secondly guide the reinforcing member (14) substantially horizontally away from the jacking area and out from under the structural foundation (22). The guide block can be built into or attached to the jack (25). Depending on the flexibility of the reinforcing member (14) and the geometry and configuration of the jacking means (24 and 25), the guide block may not be needed.

The first piling segment (12 a) is driven or jacked into excavated earth beneath the structural foundation (22) to be supported then a second piling (12 b) segment, substantially identical to the first piling segment (12 a), is slid between the guide block and the first piling segment (12 a) onto the second end (11) of the reinforcing member (14) as far as the first piling segment will allow.

The second piling segment (12 b) is then driven or jacked into excavated earth, thus driving the first piling segment (12 a) deeper below the structural foundation (22). Next, additional piling segments (12 c-12 z) are repetitively slid onto the reinforcing member (14) beneath the guide block and successively jacked each into excavated earth until a last, topmost piling segment (12 z) causes the piling to reach a desired depth or the jacking means to reach a desired reactive force. The axis of each of the central conduits is axially aligned with an adjacent conduit.

In FIG. 3 it may be seen that the guide block is removed and a piling cap (30) has been placed on the reinforcing member (14). The piling cap (30) has a substantially centrally located channel (32) through which is inserted the second end (11) of the reinforcing member (14) until the piling cap (30) is resting on top of the last piling segment (12 z). Again, it should be noted that he axis of the central conduits of each segment is aligned with the central conduit of the adjacent segment.

The second end (11) of the reinforcing member is severed a desired distance above the top of the piling cap and a tensioning device (40) is mechanically attached (or cause to be threaded) to the second end (11) of the reinforcing member (14) substantially adjacent to the top of the piling cap. Then, with a desired torque, the tensioning device is tightened on the second end (11) of the reinforcing member (14), thereby introducing a tensile force into the reinforcing member (14) and a compressive force (or columnar strength) into the captured stack or column of piling segments. The tensioning device may be as simple as a threaded nut locking down onto a threaded coupling attached to the reinforcing member. The second end (11) of the reinforcing member (14) may be severed before the piling cap is attached, or after the post-tensioning is complete.

Using the piling cap (30) as a base, the structural foundation (22) is jacked to its desired position above the piling cap (30), a spacer block or blocks (34) placed between the piling cap (30) and the structural foundation (22), the jacking means (24 and 25) removed, and the excavated area backfilled around the piling cap, spacer block, and structural foundation. Steel or metal shims may be inserted between the spacer block and the structural foundation if needed.

As an example of other embodiments (see FIGS. 4, 4A, 5, and 5B), the present invention can be practiced with more than a single reinforcing member (15 a-15 d) in or on a segmented piling (12 a). The first piling segment (12 a) could be fitted with a metallic bridle (52, FIG. 4) or basket-like device (53, FIG. 5), or an embedded device (not shown), to which multiple reinforcing members may be attached. The reinforcing members may be contained in inside channels (18) in the individual segments (FIGS. 4 and 4A), or they may extend externally (FIGS. 5 and 5A) in slots on the segment (12 x). Some or all of the reinforcing members may then be post-tensioned with means similar to that in the embodiment described above.

Alternatively, the earth may or may not be excavated such that the first piling segment is driven into excavated earth but once the second piling segment is placed on top of the first segment and driven, the first piling segment is driven into unexcavated earth. Another embodiment has the first piling segment being driven into unexcavated earth.

In another embodiment (FIG. 6), a large washer (60) may be used as part of the anchor such that it has substantially the same diameter as the piling segment. This larger washer (60) provides a protective end surface to the first piling segment (12 a) to reduce damage to the first piling segment as it is being driven into the earth. Where appropriate, a bullet shaped nose member (62) may be attached to the washer (60) and cover the anchor mechanism nut (20). This nose member (62) both protects the first piling segment (12 a) and makes it easier to drive the first piling segment into the earth.

While the reinforcing member (14) is shown (see FIG. 1) being secured beneath the segment (12 a) by the washer and nut arrangement to form the anchor mechanism (20), other means for rigidly securing the member in a manner so as to prevent removal of the first end of the reinforcing member through the first piling segment could be used. For example, the washer could be welded to the reinforcing member or a cotter pin could be inserted through the reinforcing member below the washer.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon the reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications that fall within the scope of the invention. 

1. A support system for disposition between a structural foundation and a subterranean strata comprising: a plurality of support piling segments vertically disposed in a columnar array beneath said foundation, each of said segments having a central channel extending longitudinally through a body portion of each of said segments, each of said conduits axially aligned with an adjacent conduit of one of said other segments; a tensioning member having a first end and a second end, said tensioning member slideable through said conduits the entire length of each of said segments, said first end of said tensioning member extending beyond the bottom of the first, lowermost segment of said columnar array; an anchor affixed to said first end of said tensioning member and sized such that said anchor may not pass through said conduits in said segments; and a tension adjustment mechanism affixed to said second end of said tensioning member, said second end extending above the top of the uppermost segment of said columnar array, said adjustment mechanism adapted to increase and decrease the amount of compressive force applied to said tensioning member thereby controlling the columnar strength of said support system.
 2. A method for installing a support system between a structural foundation and a subterranean strata comprising: providing a plurality of piling segments each having a central conduit extending longitudinally through a body portion of each of said segments; providing a tensioning member having a first end and a second end, said tensioning member slideable through said conduits the entire length of each of said segments; providing an anchor to be affixed to said first end of said tensioning member and sized such that said anchor may not pass through said conduits in said segments; providing a tension adjustment mechanism to be affixed to said second end of said tensioning member, said adjustment mechanism adapted to increase and decrease the amount of compressive force applied to said tensioning member; inserting said first end of said reinforcing member completely through said central channel of a first lowermost piling segment, said channel being substantially parallel to the longitudinal axis of said first piling segment, said axis being substantially perpendicular to said structural foundation when said first piling segment is in its final installed position, said reinforcing member being longer than the anticipated final depth of said system; mechanically attaching said anchor to said first end of said reinforcing member extending beyond the bottom of said first, lowermost piling segment, said anchor sized to prevent removal of said first end back through said first piling segment channel; excavating earth beneath the area of said structural foundation to be supported at least sufficient to accommodate a jacking means and said first piling segment; placing said first piling segment into excavated earth beneath said structural foundation to be supported; driving, with said jacking means, said first piling segment into excavated earth beneath said structural foundation to be supported; sliding a second of said plurality of piling segment substantially onto a second end of said reinforcing member; driving, with said jacking means, said second piling segment into said excavated earth, thereby driving said first piling segment deeper below said structural foundation; repetitively sliding additional segments of said piling segments onto said reinforcing member and successively jacking each additional segment into said excavated earth until a last, uppermost piling segment results in said support reaching said final depth; sliding a piling cap on said reinforcing member, said piling cap having a substantially centrally located channel through which is inserted said second end of said reinforcing member until said piling cap is resting on top of said last piling segment; severing said second end of the reinforcing member a desired distance above the top of said piling cap; attaching a tensioning adjustment mechanism on said second end of said reinforcing member; adjusting the tension on said reinforcing member to a desired torque; using said piling cap as a base, jacking said structural foundation to a desired position above said piling cap; placing a spacer block between said piling cap and said structural foundation; removing said jacking means; and backfilling said excavated area.
 3. A process for installing segmented post-tensioned support system underneath a structural foundation comprising: excavating earth beneath the area of said structural foundation to be supported at least sufficient to accommodate a jacking means and a first piling segment; inserting the first end of a reinforcing member completely through a centrally located channel substantially parallel to the longitudinal axis of said first piling segment, said axis being substantially perpendicular to said structural foundation to be supported when said first piling segment is in its final installed position, said reinforcing member being longer than the anticipated final depth of said system; mechanically attaching an anchor to a protruding first end of said reinforcing member, said anchor sized to prevent removal of said first end back through said first piling segment channel; placing said first piling segment into said excavated earth beneath said structural foundation to be supported; driving, with said jacking means, said first piling segment into said excavated earth beneath said structural foundation to be supported; sliding a second piling segment substantially identical to said first piling segment onto a second end of said reinforcing member; driving, with said jacking means, said second piling segment into said excavated earth, thereby driving said first piling segment deeper below said structural foundation; repetitively sliding additional piling segments substantially identical to said first piling segment onto said reinforcing member and successively jacking each additional segment into said excavated earth until a last piling segment results in said support reaching said final depth; sliding a piling cap on said reinforcing member, said piling cap having a substantially centrally located channel through which is inserted said second end of said reinforcing member until said piling cap is resting on top of said last piling segment; severing said second end of the reinforcing member a desired distance above the top of said piling cap; mechanically attaching a threaded coupling to said second end of said reinforcing member substantially adjacent to said top of said piling cap; attaching a tensioning device onto said threaded coupling on said second end of said reinforcing member; adjusting the tension on said reinforcing member to a desired torque; using said piling cap as a base, jacking said structural foundation to a desired position above said piling cap; placing a spacer block between said piling cap and said structural foundation; removing said jacking means; and backfilling said excavated area.
 4. The process of claim 3 further comprising a reinforcing member turning guide outside the perimeter of the structural foundation to be supported.
 5. The process of claim 3 whereby the second end of the reinforcing member is severed before the piling cap is attached.
 6. The process of claim 3 whereby the second end of the reinforcing member is severed a desired distance above the top of the piling cap after the tightening device is tightened onto the threaded device on the second end of the reinforcing member, thereby tensioning the reinforcing member to a desired torque;
 7. The process of claim 3 further comprising shims between the spacer block and the structural foundation. 